Methods and Behaviors

1. 4 Methods and Behaviors C# Programming: From Problem Analysis to Program Design 2nd Edition C# Programming: From Problem Analysis to Program Design

2. Chapter Objectives • Become familiar with the components of a method • Call class methods with and without parameters • Use predefined methods in the Console and Math classes • Write your own value and nonvalue-returning class methods (with and without parameters) • Learn about the different methods and properties used for object-oriented development C# Programming: From Problem Analysis to Program Design

3. Chapter Objectives (continued) • Write your own instance methods to include constructors, mutators, and accessors • Call instance methods including constructors, mutators, and accessors • Distinguish between value, ref, and out parameter types • Work through a programming example that illustrates the chapter’s concepts C# Programming: From Problem Analysis to Program Design

4. Anatomy of a Method • Methods defined inside classes • Group program statements • Based on functionality • Called one or more times • All programs consist of at least one method • Main( ) • User-defined method C# Programming: From Problem Analysis to Program Design

5. /* SquareExample.cs Author: Doyle */ using System; namespace Square { publicclass SquareExample { publicstaticvoid Main( ) { int aValue = 768; int result; result = aValue * aValue; Console.WriteLine(“{0} squared is {1}”, aValue, result); Console.Read( ); } } } Required method C# Programming: From Problem Analysis to Program Design

6. Anatomy of a Method (continued) Figure 4-1 Method components C# Programming: From Problem Analysis to Program Design

7. Modifiers • Appear in method headings • Appear in the declaration heading for classes and other class members • Indicate how it can be accessed • Types of modifiers • Static • Access C# Programming: From Problem Analysis to Program Design

8. Static Modifier • Indicates member belongs to the type itself rather than to a specific object of a class • Main( ) must include static in heading • Members of the Math class are static • public static double Pow(double, double) • Methods that use the static modifier are called class methods • Instance methods require an object C# Programming: From Problem Analysis to Program Design

9. Access Modifiers • public • protected • internal • protected internal • private C# Programming: From Problem Analysis to Program Design

10. Level of Accessibility C# Programming: From Problem Analysis to Program Design

11. Return Type • Indicates what type of value is returned when the method is completed • Always listed immediately before method name • void • No value being returned • return statement • Required for all non-void methods • Compatible value C# Programming: From Problem Analysis to Program Design

12. Return Type (continued) Return type publicstaticdouble CalculateMilesPerGallon (int milesTraveled, double gallonsUsed) { return milesTraveled / gallonsUsed; } Compatible value (double) returned C# Programming: From Problem Analysis to Program Design

13. Method Names • Follow the rules for creating an identifier • Pascal case style • Action verb or prepositional phrase • Examples • CalculateSalesTax( ) • AssignSectionNumber( ) • DisplayResults( ) • InputAge( ) • ConvertInputValue( ) C# Programming: From Problem Analysis to Program Design

14. Parameters • Supply unique data to method • Appear inside parentheses • Include data type and an identifier • In method body, reference values using identifier name • Parameter refers to items appearing in the heading • Argument for items appearing in the call • Formal parameters • Actual arguments C# Programming: From Problem Analysis to Program Design

15. Parameters (continued) • publicstaticdoubleCalculateMilesPerGallon • (int milesTraveled, double gallonsUsed) • { • return milesTraveled / gallonsUsed; • } • Call to method inside Main( ) method • Console.WriteLine(“Miles per gallon = {0:N2}”, • CalculateMilesPerGallon(289, 12.2)); Two formal parameters Actual arguments C# Programming: From Problem Analysis to Program Design

16. Parameters (continued) • Like return types, parameters are optional • Keyword void not required (inside parentheses) – when there are no parameters publicvoid DisplayMessage( ) { Console.Write(”This is “); Console.Write(”an example of a method ”); Console.WriteLine(“body. ”); return; // no value is returned } C# Programming: From Problem Analysis to Program Design

17. Method Body • Enclosed in curly braces • Include statements ending in semicolons • Declare variables • Do arithmetic • Call other methods • Value-returning methods must include return statement C# Programming: From Problem Analysis to Program Design

18. Calling Class Methods • Invoke a method • Call to method that returns no value [qualifier].MethodName(argumentList); • Qualifier • Square brackets indicate optional • class or object name • Call to method does not include data type • Use Intellisense C# Programming: From Problem Analysis to Program Design

19. Predefined Methods • Extensive class library • Console class • Overloaded methods • Write( ) • WriteLine( ) • Read( ) • Not overloaded • Returns an integer C# Programming: From Problem Analysis to Program Design

20. Intellisense After typing the dot, list of members pops up After typing the dot, list of members pops up Method signature(s) and description Method signature(s) and description 3-D fuchsia colored box —methods aqua colored box — fields (not shown) Figure 4-2 Console class members C# Programming: From Problem Analysis to Program Design

21. Intellisense Display string argument expected string parameter 18 different Write( ) methods Figure 4-3 IntelliSense display C# Programming: From Problem Analysis to Program Design

22. Intellisense Display (continued) Figure 4-4 Console.Read ( ) signature Figure 4-5 Console.ReadLine ( ) signature C# Programming: From Problem Analysis to Program Design

23. Call Read( ) Methods int aNumber; Console.Write(“Enter a single character: ”); aNumber = Console.Read( ); Console.WriteLine(“The value of the character entered: ” + aNumber); Enter a single character: a The value of the character entered: 97 C# Programming: From Problem Analysis to Program Design

24. Call Read( ) Methods (continued) int aNumber; Console.WriteLine(“The value of the character entered: “ + (char) Console.Read( )); Enter a single character: a The value of the character entered: a C# Programming: From Problem Analysis to Program Design

25. Call ReadLine( ) Methods • More versatile than the Read( ) • Returns all characters up to the enter key • Not overloaded • Always returns a string • String value must be parsed C# Programming: From Problem Analysis to Program Design

26. Call Parse( ) • Predefined static method • All numeric types have a Parse( ) method • double.Parse(“string number”) • int.Parse(“string number”) • char.Parse(“string number”) • bool.Parse(“string number”) • Expects string argument • Argument must be a number– string format • Returns the number (or char or bool) C# Programming: From Problem Analysis to Program Design

27. /* AgeIncrementer.cs Author: Doyle */ using System; namespace AgeExample { public class AgeIncrementer { publicstatic void Main( ) { int age; string aValue; Console.Write(“Enter your age: “); aValue = Console.ReadLine( ); age = int.Parse(aValue); Console.WriteLine(“Your age next year” + “ will be {0}”, ++age); Console.Read( ); } } } C# Programming: From Problem Analysis to Program Design

28. /* SquareInputValue.cs Author: Doyle */ using System; namespace Square { class SquareInputValue { staticvoid Main( ) { string inputStringValue; double aValue, result; Console.Write(“Enter a value to be squared: ”); inputStringValue = Console.ReadLine( ); aValue = double.Parse(inputStringValue); result = Math.Pow(aValue, 2); Console.WriteLine(“{0} squared is {1}”, aValue, result); } } } C# Programming: From Problem Analysis to Program Design

29. Call Parse( ) (continued) string sValue = “True”; Console.WriteLine (bool.Parse(sValue)); // displays True string strValue = “q”; Console.WriteLine(char.Parse(strValue)); // displays q C# Programming: From Problem Analysis to Program Design

30. Call Parse( ) with Incompatible Value • Console.WriteLine(char.Parse(sValue)); • when sValue referenced “True” Figure 4-6 System.FormatException run-time error C# Programming: From Problem Analysis to Program Design

31. Convert Class • More than one way to convert from one base type to another • System namespace — Convert class — static methods • Convert.ToDouble( ) • Convert.ToDecimal( ) • Convert.ToInt32( ) • Convert.ToBoolean( ) • Convert.ToChar( ) • int newValue = Convert.ToInt32(stringValue); C# Programming: From Problem Analysis to Program Design

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34. C# Programming: From Problem Analysis to Program Design

35. Math( ) Class Each call returns a value • double aValue = 78.926; • double result1, • result2; • result1 = Math.Floor(aValue); // result1 = 78 • result2 = Math.Sqrt(aValue); // result2 = 8.88403061678651 • Console.Write(“aValue rounded to 2 decimal places” • + “ is {0}”, Math.Round(aValue, 2)); aValue rounded to 2 decimal places is 78.93 C# Programming: From Problem Analysis to Program Design

36. Method Calls That Return Values In an assignment statement Line 1int aValue = 200; Line 2int bValue = 896; Line 3int result; Line 4 result = Math.Max(aValue, bValue); // result = 896 Line 5 result += bValue * Line 6 Math.Max(aValue, bValue) – aValue; // result = 896 + (896 * 896 - 200) (result = 803512) Line 7 Console.WriteLine(“Largest value between {0} ” Line 8 + “and {1} is {2}”, aValue, bValue, Line 9 Math.Max(aValue, bValue)); Part of arithmetic expression Argument to another method call C# Programming: From Problem Analysis to Program Design

37. Writing Your Own Class Methods • [modifier(s)] returnType  MethodName ( parameterList ) • {  • // body of method - consisting of executable statements    • } • void Methods • Simplest to write • No return statement C# Programming: From Problem Analysis to Program Design

38. class method Writing Your Own Class Methods – void Types public staticvoid DisplayInstructions( ) { Console.WriteLine(“This program will determine how ” + “much carpet to purchase.”); Console.WriteLine( ); Console.WriteLine(“You will be asked to enter the ” + “ size of the room and ”); Console.WriteLine(“the price of the carpet, ” + ”in price per square yards.”); Console.WriteLine( ); } A call to this method looks like: DisplayInstructions( ); C# Programming: From Problem Analysis to Program Design

39. Writing Your Own Class Methods – void Types (continued) • public static void DisplayResults(double squareYards, • double pricePerSquareYard) • { • Console.Write(“Total Square Yards needed: ”); • Console.WriteLine(“{0:N2}”, squareYards); • Console.Write(“Total Cost at {0:C} “, pricePerSquareYard); • Console.WriteLine(“ per Square Yard: {0:C}”, • (squareYards * pricePerSquareYard)); • } • static method called from within the class where it resides • To invoke method – DisplayResults(16.5, 18.95); C# Programming: From Problem Analysis to Program Design

40. Value-Returning Method • Has a return type other than void • Must have a return statement • Compatible value • Zero, one, or more data items may be passed as arguments • Calls can be placed: • In assignment statements • In output statements • In arithmetic expressions • Or anywhere a value can be used C# Programming: From Problem Analysis to Program Design

41. Value-Returning Method (continued) public staticdouble GetLength( ) { string inputValue; int feet, inches; Console.Write(“Enter the Length in feet: ”); inputValue = Console.ReadLine( ); feet = int.Parse(inputValue); Console.Write(“Enter the Length in inches: “); inputValue = Console.ReadLine( ); inches = int.Parse(inputValue); return (feet + (double) inches / 12); } Return type→ double double returned C# Programming: From Problem Analysis to Program Design

42. CarpetExampleWithClassMethods /* CarpetExampleWithClassMethods.cs */ using System; namespace CarpetExampleWithClassMethods { publicclass CarpetWithClassMethods { publicstaticvoid Main( ) { double roomWidth, roomLength, pricePerSqYard, noOfSquareYards; DisplayInstructions( ); // Call getDimension( ) to get length roomLength = GetDimension(“Length”); C# Programming: From Problem Analysis to Program Design

43. CarpetExampleWithClassMethods (continued) /* CarpetExampleWithClassMethods.cs */ using System; namespace CarpetExampleWithClassMethods { publicclass CarpetWithClassMethods { C# Programming: From Problem Analysis to Program Design

44. publicstaticvoid Main( ) { double roomWidth, roomLength, pricePerSqYard, noOfSquareYards; DisplayInstructions( ); // Call getDimension( ) to get length roomLength = GetDimension(“Length”); roomWidth = GetDimension(“Width”); pricePerSqYard = GetPrice( ); noOfSquareYards = DetermineSquareYards(roomWidth, roomLength); DisplayResults(noOfSquareYards, pricePerSqYard); } C# Programming: From Problem Analysis to Program Design

45. public staticvoid DisplayInstructions( ) { Console.WriteLine(“This program will determine how much " + “carpet to purchase.”); Console.WriteLine( ); Console.WriteLine("You will be asked to enter the size of ” + “the room "); Console.WriteLine(“and the price of the carpet, in price per” + “ square yds.”); Console.WriteLine( ); } C# Programming: From Problem Analysis to Program Design

46. publicstaticdouble GetDimension(string side ) { string inputValue; // local variables int feet, // needed only by this inches; // method Console.Write("Enter the {0} in feet: ", side); inputValue = Console.ReadLine( ); feet = int.Parse(inputValue); Console.Write("Enter the {0} in inches: ", side); inputValue = Console.ReadLine( ); inches = int.Parse(inputValue); // Note: cast required to avoid int division return (feet + (double) inches / 12); } C# Programming: From Problem Analysis to Program Design

47. public staticdouble GetPrice( ) { string inputValue; // local variables double price; Console.Write(“Enter the price per Square Yard: "); inputValue = Console.ReadLine( ); price = double.Parse(inputValue); return price; } C# Programming: From Problem Analysis to Program Design

48. public staticdouble DetermineSquareYards (double width, double length) { constint SQ_FT_PER_SQ_YARD = 9; double noOfSquareYards; noOfSquareYards = length * width / SQ_FT_PER_SQ_YARD; return noOfSquareYards; } public staticdouble DeterminePrice (double squareYards, double pricePerSquareYard) { return (pricePerSquareYard * squareYards); } C# Programming: From Problem Analysis to Program Design

49. public staticvoid DisplayResults (double squareYards, double pricePerSquareYard) { Console.WriteLine( ); Console.Write(“Square Yards needed: ”); Console.WriteLine("{0:N2}", squareYards); Console.Write("Total Cost at {0:C} ", pricePerSquareYard); Console.WriteLine(“ per Square Yard: {0:C}”, DeterminePrice(squareYards, pricePerSquareYard)); } } // end of class } // end of namespace C# Programming: From Problem Analysis to Program Design

50. CarpetExampleWithClassMethods (continued) Figure 4-7 Output from CarpetExampleWithClassMethods C# Programming: From Problem Analysis to Program Design